(1) Field of the Invention
This invention relates generally to three dimensional electronic imaging systems. This invention also relates generally to endoscopes, which are employed in medicine for imaging selective body regions and for facilitating the delivery of high-energy radiation for treatment purposes. More particularly, the present invention relates generally to endoscopes which employ fiber optic channels and which employ lasers or other high-energy radiation sources.
(2) Prior Art and Pertinent Technology
Stereoscopy is a function of the mental interpretation of two slightly different images viewed by the two eyes of an observer. The mental interpretation is based on the experience of the observer. Stereo imagery has been demonstrated on television systems. The stereo images are shown on the television display with one perspective displayed in even fields and the other perspective displayed in odd fields. Special glasses are employed so that one eye of the observer views the even fields and the other eye views the odd fields. The cognitive faculties of the observer processes the two dimensional images to provide a perceived three dimensional image.
Stereo image acquisition has been obtained by numerous techniques. One technique disclosed in an article by Yakimovsky and Cunningham entitled "A System for Extracting Three Dimensional Measurements from a Stereo Pair of TV Cameras", published in Computer Graphics and Image Processing 7, page 195-210, 1978, employs a stereo pair of TV cameras which are precisely laterally spaced so as to obtain a stereo perspective at a desired distance. In X-ray diagnostic radiology, the X-ray source may be displaced from one position to another position for two successive exposures. The radiation sensor is stationary. The two images are conventionally filmed. The film images can be viewed on a typical stereoscope. The images can also be read into a digital video system for viewing on a stereo video display such as described above. In conventional stereo imagery, the object is uniformly illuminated and the images are acquired entirely in a two dimensional format--typically by means of photographic film or a TV camera.
Lateral effect photodiodes are routinely employed as position sensors for applications in which a light source can be attached to the object of interest. The lateral effect diodes are capable of resolving the position of an incident light spot to thereby determine the position of the object. In automated manufacturing operations, electronic systems which employ lateral effect photodiodes are used to track robot arms and other objects that are involved in the manufacturing process.
In conventional stereo imaging, correlating and calculating the data obtained from two stereo images to extract the third dimension or elevation (depth) information, is a fairly complex task which ordinarily involves extensive post detection processing. Conventional stereo imaging techniques employ two images taken at slightly different angles from the object. A cross-correlation number then is applied to the two images for determining the lateral shift of each pixel in the image. The lateral shift corresponds to the displacement (third dimension) of the given pixel for the object. The processing procedure is limited by the ability to cross-correlate pixels from the two different images. Objects having low contrast and very little high frequency detail frequently result in a significant amount of ambiguous correlation. In addition, the processing is a computationally exhausting task--especially for large images.
For some applications, the size of the image sensing components is of paramount importance. Typically stereo imaging requires two photographic or video cameras. The video cameras may take the form of conventional video tubes or solid state CCD chips. Even though the CCD chips have a relatively small size, the CCD chips are not practical for use in acquiring stereo images in applications such as those requiring small diameter endoscopes.
The new and improved endoscope and associated system of the present invention has particular applicability in medicine for many procedures such as those that use a gastroscope, sigmoidoscope, uretheroscope, laryngoscope, and bronchoscope. The invention also has applicability in connection with industrial applications, such as, for example, remote focus flexible fiberscopes, micro-borescopes, and micro-fiberscopes.
Conventional endoscopes typically employ incoherent bundles of optical fibers for transmitting light rays (typically white light) from a proximal end of a tubular instrument to the distal end. Typically, a pair of diametral channels are employed for illuminating an object to be imaged. A separate coherent flexible fiber optic channel communicates from the distal end to the proximal end with an eyepiece, television camera, photographic camera or other imaging devices for providing an image. For relatively large diameter endoscopes, a separate flexible-fiber quartz channel may be employed for transmitting a high-powered beam of laser radiation to an object for therapeutic purposes. An auxiliary channel may traverse the tubular endoscope for receiving various instruments for severing and retrieving selected tissue. In addition, the endoscope may contain channels which provide for water and air communication with the distal end of the endoscope.
Conventional endoscopes provide a reasonably high quality image especially enlarged-diameter endoscopes. Conventional endoscopes are quite versatile and perform a large variety of useful functions. The conventional endoscopic optic systems, however, do exhibit a number of deficiencies. When viewing objects under high resolution, the image may exhibit a mesh or chicken-wire effect wherein individual groupings of fibers are outlined. Conventional endoscopes also exhibit some degree of loss of contrast associated with scatter intrinsic to the illumination of the object, and also some loss of contrast due to veiling glare of the multiple optical components. The space requirements, e.g., the diameter of the endoscope, represents a design constraint which is significant when separate illumination and imaging channels are employed. Such a constraint may be quite critical for vascular endoscopes which image interior arteries having diameters on the order of two millimeters or less. Another constraint of the conventional endoscopic optic systems is that they do not provide an optical system which facilitates stereo or three dimensional imaging, or the opportunity to acquire multi-spectral-multi-dimensional images, simultaneously.
The imaging channel of a conventional endoscope may be coupled to a television camera or the television camera may be employed in conjunction with an eyepiece by means of an optical beam splitter. The video signal output from the television camera is fed to a television monitor and/or a video recorder of a digital image acquisition system for processing, display and archival storage. The television camera may be a conventional television tube, a solid state video camera employing CCD chips, or other conventional forms.
Sato U.S. Pat. No. 4,604,992 discloses a CCD video camera chip at the distal end of the endoscope. The disposition of the CCD chip obviates the use of the coherent fiber optic bundle for imaging, and thus, provides a system which produces an image not susceptible to the chicken-wire effect or to individually broken fibers which cause pixel dropout. The size of the CCD chip, however, limits the minimal diameter of the endoscope. The CCD video camera chip also allows for the passage of high energy laser radiation to be trained on the object for therapy while the object is concurrently viewed through the CCD imaging camera.
Karaki et al U.S. Pat. No. 4,808,636 discloses a solid state type of imaging sensor position at the proximal end of the endoscope. The analog video signal is converted to a digital signal. The digital signal is then processed to eliminate the chicken-wire or mesh effect and to account for the pixel dropout in the displayed image. Pixel dropout commonly results from broken fibers in the fiber optic bundle. The spacial resolution for the conventional endoscope is essentially determined by the diameter of the optical fibers and the magnification of the imaging optics. In general, the commonly employed fibers have diameters in the range of eight to ten microns for high-resolution endoscopes.
Other references which are related to the general field of the invention are identified by patentee and patent number as follows:
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